Monostable multivibrator



Ap 1967 HlDEYA NISHIOKA MONOSTABLE MULTIVIBRATOR Filed July 30. 1964 l Eoe Cl8(R27+R26) e R27+R26 @LIS' United States Patent Ofliice 3,315,99 Patented Apr. 18, 1967 3,315,099 MGNUSTABLE MULTIVJBRATOR Hideya Nishiolta, Kawasaki, Japan, assignor to Fujitsu Limited, Kawasaki, Japan, a corporation of Japan Filed Juiy 3t), 1964, Ser. No. 386,123 Claims priority, application Japan, July 30, 1963, Si /40AM) 5 Claims. (Cl. Mil-88.5)

My invention relates to a multivibrator. More particularly, the invention relates to a transistorized monostable multivibrator circuit.

An object of the invention is to provide a new and improved monostable multivibrator circuit.

Another object of the invention is to provide a monostable multivibrator circuit having a stable oscillation frequency.

Still another object of the invention is to provide a monostable multivibrator circuit of simple structure having a stable oscillation frequency.

In a monostable multivibrator circuit of known type comprising transistors or vacuum tubes, the positive feedback circuit includes transistors or vacuum tubes, and when one circuit branch is in conductive condition the other circuit branch is in non-conductive condition. The voltage or current signal for changing the non-conductive branch to conductive condition and for changing the conductive branch to non-conductive condition, is applied to the branch in conductive condition through a time constant circuit which changes the branch in conductive condition to non-conductive condition. Then, using the cutoff characteristic of the vacuum tube or the transistor, after a period of time determined by the time constant has passed, the non-conductive branch is changed to the conductive condition again.

The time required to return the circuit to its conductive condition after the application of the signal to the circuit branch in conductive condition to change said branch in conductive condition to its non-conductive condition varies considerably due to the cut-oil. characteristic of the transistor or the vacuum tube or due to the supply or power voltage in a known type of multivibrator. This time is known as the operating time, and it may vary from about i% to i50% in normal operation. When a transistor is utilized, the change of the cut-off characteristic of the transistor due to changes in temperature, greatly influences the operating time and it is difiicult to attain stable operation.

The present invention eliminates such disadvantages and provides a multivibrator circuit having an operating time which is influenced very little, if at all, by changes of ambient temperature or supply or power voltage. The operating time is chiefly determined by the value of the time constant circuit and is not influenced by the cut-off characteristic of the transistor or the vacuum tube or by the supply of power voltage. Thus, in the monostable multivibrator circuit of the present invention, changes in the operating time may be kept to less than il% of the designated value in normal operation and the stability of operation is very greatly improved.

In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, wherein:

FIG. 1 is a circuit diagram of an embodiment of the monostable multivibrator circuit of the present invention;

FIG. 2 is a graphical illustration of wave shapes present in the embodiment of FIG. 1; and

FIG. 3 is a circuit diagram of a modification of the embodiment of FIG. 1.

In FIG. 1, each of the transistors 11 and 12 has an emitter electrode, a collector electrode and a base electrode. The transistor 11 is maintained in conductive con- 1y more negative than dition by a base bias voltage provided by a source of supply voltage via power terminal or input voltage supply terminal 13 and a resistor 14. The collector voltage of the transistor 11 is always maintained at a potential slightground potential due to the voltage drop across a resistor 15.

The transistor 12 is always biased beyond non-conductive or cut-off condition by a positive base bias voltage provided by a source of supply voltage via input voltage supply terminal 16 and a resistor 17. The voltage provided at the terminals 13 and 16 may come from the same source of supply voltage or different sources of supply voltage. The transistor 12 is thus maintained in its nonconductive condition and the circuit is maintained stable in this condition. A condenser 18 is charged to a value equal to the magnitude of the supply or power voltage E0 through a diode 19, the resistance between the emitter and base of the transistor 11, and a part. of the resistance of a potentiometer 21 determined by the tap 22 of said potentiometer and extending between said tap and the input terminal 13.

When an external signal is applied to the circuit arrangement via terminal 23 it changes the transistor 11 from its conductive condition to its non-conductive condition. The signal applied via the terminal 23 is applied to the base electrode of the transistor 11 via a diode .24. The voltage drop across the resistor 15, effecting the collector current transistor 11, is eliminated and the: collector potential of the transistor 11 becomes almost equal to the power or supply voltage E0. The base of the transistor 12 is rapidly biased to a negative potential and the transistor 12 is changed from its non-conductive condition to its conductive condition.

A voltage drop effecting the collector current of the transistor 12 then appears across the potentiometer 21 and the potential at its tap 22 becomes positive relative tothe potential of a point 25 between the charged capacitor 18, on one hand, and the diode 19 and a resistor 26, on the other hand. A voltage in the reverse direction is thus applied to the diode 19 which thus becomes non-conductive. The capacitor 18 then discharges through the resistor 26 and the collector-emitter path of the transistor 12, and resistor 27.

FIG. 2a illustrates the change of voltage E18 of the condenser 18 in the afore-discussed situation and FIG. 2b illustrates the change of charging or discharging current 118 of said condenser. If the time period which passes after the transistor 12 reaches its conductive condition until the discharging of the capacitor 18 is started, is t, then, as shown in FIG. 2, t is less than zero. That is, before the discharging starts, the voltage E18 of the capacitor 18 is equal to the power or supply voltage E0. The time period t is greater than zero. That is, after discharging starts, the voltage E18 changes with the passing of time in accordance with the equation The discharging current 1'18 is zero when t is less than zero and changes in accordance with the equation tor 18, 2 being the base of the natural If the capacitor 18 tive potential at the logarithm. continues to discharge, the negaterminal 25 decreases in a time period 12 and becomes smaller than the potential ratio kEo determined by the tap 22 of the potentiometer 21. The diode 19 then becomes conductive and the discharging of the capacitor 18 will stop. After expiration of the time period t2, the potential of the terminal 25 is maintained at the constant value of kEo. The discharging current i113 of the capacitor 18 thus becomes rapidly zero when t:r2, and the bias of the transistor 11 drops to below its cut-off value. The transistor 11 therefore rapidly becomes conductive. As a result, the collector potential of the transistor 11 attains a magnitude near ground potential and the base potential of the transistor 12 rapidly becomes positive.

The transistor 12 therefore becomes non-conductive and returns to the stable condition of the circuit before the external signal was applied to the terminal 23. The capacitor 18 is then rapidly charged to E0 through the base circuit of the transistor 11, the diode 19 and part of the potentiometer 21. The time t2 thus becomes the operating time of the monostable multivi-brator.

The time period 22 constitutes a value of time t which satisfies the equation.

wherein it is the potential ratio of the potentiometer 21.

The operating time 12 thus depends only upon the resistance R27 of the resistor 27, the resistance R26 of the resistor 26, the capacitance CllS of the capacitor 18 and the potential ratio k of the potentiometer 2'1, and is not dependent upon the power or supply voltage E0 or the characteristics of the transistors 11 and 12. Practically, it is easy to reduce changes in the constancy of the resistances 27 and 26, the capacitance 18 and the ratio It due to temperature or time, and therefore the operating time t2 of the monostable multivibrator may be held to the same stability as the rate of change of the constant ratio k. Accordingly, the stability of the monostable multivibrator of the present invention may be improved considerably over known types of monostable multivibrator in which the stability changes considerably due to changes in the power or supply voltage or in the characteristics of the transistors.

The operating time t2 may be changed by changing the resistance R27 of the resistor 27, by changing the resistance R26 of the resistor 26 or by changing the capacitance C18 of the capacitor 18. The operating time t2 may also be changed continuously by changing the potential dividing ratio k of the potentiometer 21.

FIG. 3 is a modification of the embodiment of FIG. 1. In FIG. 3, the same effect as in the embodiment of FIG. 1 is obtained by directly connecting the collector electrode of the transistor 12/ to the capacitor 18' via a diode 28 instead of through the potentiometer 21 and .by directly connecting said potentiometer between the input terminal 13 and ground instead of between said input terminal and the collector electrode of the transistor 12'. The potentiometer 21' and a diode 29 function in the same manner as the potentiometer 21 and the diode 19 of FIG. 1.

The diode 28 ensures the rapid charging of the capacitor 18 when the transistor 12' changes from its conductive condition to its non-conductive condition. The modification of FIG. 3 is convenient for providing different operating times 22 by changing the potential ratio of the potentiometer 21.

In the foregoing disclosure, it is assumed that the condenser 18 or 18 is charged in the stable condition of the circuit and is discharged in the unstable condition of the circuit. However, the same effect will be obtained in the circuit arrangement of the present invention in which the condenser 18 or 18 is discharged in the stable condition of the circuit and is charged in the unstable condition of the circuit. Furthermore, the circuit arrangement will function as described if vacuum tubes are utilized instead of transistors.

While the invention has been described by means of specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. A monostable multivibrator circuit arrangement having an operating time which remains stable despite variations in ambient temperature and supply voltage, comprising first and second electronic switching devices each adapted to be biased to operative conditions determining a stable state and an unstable state of said multivibrator circuit arrangement;

a source of supply voltage;

a time constant circuit comprising a capacitor and a first resistor and a second resistor together providing both a charging and discharging path for said capacitor with said source of supply voltage and coupling said first switching device to said second switching device in a manner whereby said capacitor is alternately charged and discharged and determines the operative condition of said first and second electronic switching devices; and

control means connected to said source of supply voltage providing a voltage ratio and coupled to said capacitor for stopping the charging of said capacitor when the voltage across the said capacitor equals the voltage ratio provided by said control means thereby reducing the charging current in said capacitor, the voltage across said capacitor remaining equal to said voltage ratio and the operative condition of said first and second switching devices changing said multivibrator circuit arrangement from the unstable state to the stable state due to the reduction of charging current in said capacitor, said monostable multivibrator circuit arrangement having an operating time determined by the capacitance of said capacitor, the resistance of said first and second resistors and the ratio of the voltage provided by said control means.

2. A monostable multivibrator circuit arrangement having an operating time which remains stable despite variations in ambient temperature and supply voltage, comprising first and second transistors each having emitter, collector and base electrodes and adapted to be biased to operative conditions determining a stable state and an unstable state of said multivibrator circuit arrangement;

a source of supply voltage;

a time constant circuit comprising a capacitor and a first resistor and a second resistor together providing both a charging and discharging path for said capacitor with said source of supply voltage and coupling said first transistor to said second transistor in a manner whereby said capacitor is alternately charged and discharged and determines the operative condition of said first and second transistors; and

variable potentiometer means connected to said source of supply voltage providing a voltage ratio and coupled to said capacitor for stopping the charging of said capacitor when the voltage across the said capacitor equals the voltage ratio provided by said variable potentiometer means thereby reducing the charging current in said capacitor, the voltage across said capacitor remaining equal to said voltage ratio and the operative condition fo said first and second transistors changing said multivibrator circuit arrangement from the unstable state to the stable state due to the reduction of charging current in said capacitor, said monostable multivibrator circuit arrangement having an operating time determined by the capacitance of said capacitor, the resistance of said first and second resistors and the ratio of the voltage provided by said variable potentiometer means.

3. A monostable multivibrator circuit arrangement having an operating time which remains stable despite variations in ambient temperature and supply voltage, comprising first and second electronic switching a source of supply voltage;

resistance means including first resistance means connecting said first switching device across said source of supply voltage;

resistance means connecting said second switching device across said source of supply voltage;

second resistance means connected to said second switching device;

a capacitor coupling said first and second switching devices and connected to and determining with said first and second resistance means a time constant, said first and second resistance means together providing both a charging path and a discharging path for said capacitor; and

control means connected to said source of supply voltage providing a voltage ratio and coupled to said capacitor for controlling the voltage across said capacitor, said monostable multivibrator circuit arrangement having an operating time determined by the capacitance of said capacitor, the resistance of said first and second resistance means and the ratio of the voltage provided by said control means.

4. A monostable multivibrator circuit arrangement having an operating time which remains stable despite variations in ambient temperature and supply voltage, comprising first and second transistors lector and base electrodes;

a source of supply voltage;

resistance means including first resistance means conmeeting said first transistor across said source of supply voltage;

resistance means Connecting said second transistor across said source of supply voltage;

second resistance means connected to said second transistor;

a capacitor coupling said first and second transistors and connected to and determining with said first and second resistance means a time constant, said first and second resistance means together providing both a charging path and a discharging path for said capacitor; and

devices;

each having emitter, colpotentiometer means connected to said source of supply having an operating time which remains stable despite variations in ambient temperature and supply voltage,

comprising a first transistor having emitter, collector and base electrodes, an emitter-collector path and a collectorbase path; second transistor having emitter, collector and base electrodes, an emitter-collcctor path and a collectorbase path;

a source of supply voltage;

first resistor connected in series with the collector base path of said first transistor across said source of supply voltage;

second resistor connected to the collector of said second transistor;

third resistor connected collector path of said source of supply voltage; fourth resistor connected in series with the collectorbase path of said second transistor across said source of supply voltage;

capacitor connected between said second resistor and the base electrode of said first transistor and said first resistor and determining with said first and second resistors a time constant, said first and second resistance means together providing both a charging path and a discharging path for said capacitor; and

in series with the emitterfirst transistor across said potentiometer means connected to said source or" supply voltage and having a tap determining a voltage ratio and coupled by a diode to said capacitor for controlling the voltage across said capacitor, said monostable multivibrator circuit arrangement having an operating time determined by the capacitance of said capacitor, the resistance of said first and second resistors and the ratio of the voltage across said potentiometer means determined by its tap.

References (fitted by the Examiner UNITED STATES PATENTS 2,941,096 6/1960 Gunkle 307-88.5 2,976,432 3/1961 Geclcle 30788.5 3,107,309 10/1963 Hitt 30788.5 3,227,891 1/1966 Ashcraft 30788.5

ARTHUR GAUSS, Primary Examiner. R. H. EPSTEIN, Assistant Examiner. 

1. A MONOSTABLE MULTIVIBRATOR CIRCUIT ARRANGEMENT HAVING AN OPERATION TIME WHICH REMAINS STABLE DESPITE VARIATIONS IN AMBIENT TEMPERATURE AND SUPPLY VOLTAGE, COMPRISING FIRST AND SECOND ELECTRONIC SWITCHING DEVICES EACH ADAPTED TO BE BIASED TO OPERATIVE CONDITIONS DETERMINING A STABLE STATE AND AN UNSTABLE STATE OF SAID MULTIVIBRATOR CIRCUIT ARRANGEMENT; A SOURCE OF SUPPLY VOLTAGE; A TIME CONSTANT CIRCUIT COMPRISING A CAPACITOR AND A FIRST RESISTOR AND A SECOND RESISTOR TOGETHER PROVIDING BOTH A CHARGING AND DISCHARGING PATH FOR SAID CAPACITOR WITH SAID SOURCE OF SUPPLY VOLTAGE AND COUPLING SAID FIRST SWITCHING DEVICE TO SAID SECOND SWITCHING DEVICE IN A MANNER WHEREBY SAID CAPACITOR IS ALTERNATELY CHARGED AND DISCHARGED AND DETERMINES THE OPERATIVE CONDITION OF SAID FIRST AND SECOND ELECTRONIC SWITCHING DEVICES; AND CONTROL MEANS CONNECTED TO SAID SOURCE OF SUPPLY VOLTAGE PROVIDING A VOLTAGE RATIO AND COUPLED TO SAID CAPACITOR FOR STOPPING THE CHARGING OF SAID CAPACITOR WHEN THE VOLTAGE ACROSS THE SAID CAPACITOR EQUALS THE VOLTAGE RATIO PROVIDED BY SAID CONTROL MEANS THEREBY REDUCING THE CHARGING CURRENT IN SAID CAPACITOR, THE VOLTAGE ACROSS SAID CAPACITOR REMAINING EQUAL TO SAID VOLTAGE RATIO AND THE OPERATIVE CONDITION OF SAID FIRST AND SECOND SWITCHING DEVICES CHANGING SAID MULTIVIBRATOR CIRCUIT ARRANGEMENT FROM THE UNSTABLE STATE TO THE STABLE STATE DUE TO THE REDUCTION OF CHARGING CURRENT IN SAID CAPACITOR, SAID MONOSTABLE MULTIVIBRATOR CIRCUIT ARRANGEMENT HAVING AN OPERATING TIME DETERMINED BY THE CAPACITANCE OF SAID CAPACITOR, THE RESISTANCE OF SAID FIRST AND SECOND RESISTORS AND THE RATIO OF THE VOLTAGE PROVIDED BY SAID CONTROL MEANS. 